If you’ve been driving your car for a while, you may have encountered a situation where your “check engine” light comes on. One of the most common reasons for this is a P0420 fault code.
I’m John Cunningham, a qualified mechanic, you are in the right place, and very shortly, you’ll have a good understanding of the cause, the diagnosis process, and the fix.
We’ll cover the following:
What is P0420?
P0420 is a diagnostic trouble code (DTC) that indicates a problem with your vehicle’s catalytic converter on Bank One. The catalytic converter is responsible for reducing the emissions produced by your engine, and a faulty converter can result in higher levels of harmful gases being released into the atmosphere.
Here are the top symptoms of a P0420 fault code:
- Check Engine Light: The most common symptom of a P0420 code is the illumination of the check engine light on your dashboard.
- Reduced Engine Performance: If your catalytic converter is clogged or damaged, it can cause a reduction in engine power, resulting in a sluggish driving experience.
- Poor Fuel Economy: A faulty catalytic converter can also cause your vehicle to use more fuel than normal.
- Smell of Rotten Eggs: If your catalytic converter is not working correctly, you may notice a strong smell of rotten eggs coming from your vehicle’s exhaust.
- Failed Emissions Test: If you fail an emissions test, it could be due to a faulty catalytic converter.
- Rough Idling: If your engine is idling roughly or shaking, it could indicate a problem with your catalytic converter.
- Misfiring: A P0420 fault code can also cause your engine to misfire or run roughly.
What Causes P0420?
There are several potential causes of a P0420 fault code, including:
- Oxygen sensor issues: A faulty oxygen sensor can cause incorrect readings and trigger a P0420 code. This can happen if the oxygen sensor is dirty or contaminated or if it’s simply worn out.
- Failed catalytic converter: This is the most common cause of a P0420 code. A catalytic converter can fail due to age, high mileage, or exposure to oil or coolant. A failed catalytic converter can’t effectively reduce emissions, leading to a P0420 code.
- Exhaust leaks: Leaks in the exhaust system can cause a P0420 code. These leaks can allow air to enter the system and disrupt the readings of the oxygen sensors, leading to an incorrect reading.
- Fuel system issues: Problems with the fuel system, such as a clogged fuel injector or a faulty fuel pressure regulator, can cause a P0420 code.
- Ignition system issues: An ignition system issue, such as a faulty spark plug or ignition coil, can cause incomplete combustion and trigger a P0420 code.
How to Diagnose P0420
To diagnose a P0420 code, a mechanic will typically perform the following steps:
- Use a code scanner to retrieve the code and any other related codes.
- Inspect the exhaust system for damage, leaks, or signs of wear.
- Check the oxygen sensors for proper operation and accuracy.
- Check the catalytic converter for damage or deterioration.
- Inspect the fuel and ignition systems for any issues that could be affecting emissions.
- Check for any other related codes or issues that could be contributing to the P0420 code.
Common Fix for P0420
The most common fix for a P0420 code is to replace the catalytic converter. However, it’s important to diagnose the underlying cause of the code before replacing the converter, as the issue could be something else entirely.
Other potential fixes include:
- Replacing the oxygen sensors
- Fixing any exhaust leaks
- Cleaning or replacing the fuel injectors
- Replacing the spark plugs and ignition coils
- Cleaning or Replacing the Mass Air Flow Sensor
P0420 code is an indication that there’s an issue with the catalytic converter or the emissions system in your vehicle. It’s important to diagnose the underlying cause of the code to determine the best course of action. This may involve inspecting the exhaust system, oxygen sensors, fuel and ignition systems, and other related components.
While a failed catalytic converter is the most common cause of a P0420 code, it’s not always the case. Therefore, it’s important to have a thorough diagnosis before spending money on any repairs.
About the Author
This article was created with the assistance of AI technology to aid the author, John Cunningham, who is a seasoned Red Seal-certified auto technician with more than 25 years of experience in vehicle repairs. However, please note that John Cunningham has edited the content to ensure accuracy and quality.
You may find the following links helpful:
- How to use a fault code reader (video)
- Fault code reader I recommend for DIYers
- Fault code index page
- Beginner DIY maintenance page
- DIY troubleshooting and repair page
- Recommended mechanics tools
- Are OBD scanners universal?
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- About the Author
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John Cunningham is an Automotive Technician and writer on Rustyautos.com. He’s been a mechanic for over twenty-five years and has worked for GM, Volvo, Volkswagen, Land Rover, and Jaguar dealerships.
John uses his know-how and experience to write fluff-free articles that help fellow gearheads with all aspects of vehicle ownership, including maintenance, repair, and troubleshooting.